docs: def concrete_descendents(parentclass):
      """
      Return a dictionary containing all subclasses of the specified
      parentclass, including the parentclass.  Only classes that are
      defined in scripts that have been run or modules that have been
      imported are included, so the caller will usually first do ``from
      package import *``.
  
      Only non-abstract classes will be included.
      """
      return dict((c.__name__,c) for c in descendents(parentclass)
                  if not _is_abstract(c))